In the manufacture of creped wadding, such as facial tissues, the paper webs are would onto a spool (reel spool) at very high speeds. Because many of the lighter weight webs are fragile, it is extremely important that all of the apparatus be properly synchronized so that differences in the rotational speeds of various rolls and drums do not cause breakage of the web. For this reason, many prior processes did not include the step of calendering prior to winding the web on the soft roll. Instead, the web was calendered in the preparation of the hard rolls, where the speed of the web could be more easily controlled without coordinating with the front end of the papermaking process. In general, any added process steps, such as calendering, will decrease overall efficiency of the process.
One of the difficulties caused by the calendering step is the formation of a "bubble" at the exit of the calender nip. This bubble results from compaction of the creped web, which causes the crepe to flatten out to a certain degree, essentially making the web longer in the machine direction. This condition translates into higher web speeds after the calender rolls for which compensation must be made at the wind-up operation. In addition, this condition causes the web to flutter when there is a substantial open draw between the calender nip and the reel spool, which also is an undesirable situation.
Nevertheless, calendering prior to the soft roll is not a novel concept. For example, it is known to calender the web prior to being wound onto a reel spool driven by a single reel drum. This method is illustrated by U.S. Pat. No. 4,179,330 to Page, which teaches the use of two horizontally-oriented calender rolls, one of which forms a nip with the single reel drum. However, this configuration is known to require a more difficult threading operation which can decrease overall operating efficiency.